Properties of organic semiconductors have been studied in a search for new types of active electronic devices, such as polymeric transistors TFT (Thin Film Transistor). Polymeric deposition techniques are intrinsically low cost, relatively simple and compatible with substrates of flexible plastic or glass. These techniques allow electronic devices to be obtained with new and useful characteristics that cannot be found in devices obtained with current technologies using silicon.
Many different models of organic transistors are available [References 1-6]. In semiconductor circuits formed on silicon substrates, both N-type transistors and P-type transistors are normally present. Thus, it should be possible theoretically to form electronic circuits with organic transistors using the same electrical schemes that are used with transistors defined on silicon by simply substituting silicon P or N-type transistors with organic P or N-type transistors. Unfortunately, this is not currently possible because there are no organic N-type transistors having adequate stability and with a sufficiently large mobility of the carriers [References 11-13].
As a consequence, the present circuit schemes in CMOS technology cannot be used for forming circuits with organic transistors because these transistors may be only of P-type conductivity. Several architectures of logic gates and of simple logic circuits (ring oscillators, flip-flops, multiplexers and demultiplexers) that use OTFT (Organic Thin Film Transistor) are disclosed [Reference 7]. U.S. published patent application no. 2005/0277240 discloses architectures of logic gates of this kind made with organic field effect transistors.
Analog electronic circuits formed with organic transistors are much less frequently discussed in the literature. Japanese published patent application no. 2006,013108 discloses architectures of logic gates and of an analog amplifier that use only organic P-type transistors. The architecture of the analog amplifier is the classic architecture of a two-stage source follower The drawbacks of such an architecture are its high complexity, and the fact that it uses resistors instead of load transistors.